So far, Adobe's investigation has revealed that attackers managed to access Adobe customer IDs and encrypted passwords, as well as obtain information on 2.9 million customers, including names, encrypted credit or debit card numbers with their expiration dates, and other customer order details.

"At this time, we do not believe the attackers removed decrypted credit or debit card numbers from our systems," Arkin said.

"Our investigation to date indicates that the cyber attackers removed certain customer information between September 11 and September 17, 2013," an Adobe spokeswoman said via email. As far as the timeline for the source-code compromise is concerned, the investigation is ongoing, she said.

It's not clear if the same attackers are responsible for the compromise of customer information and accounts and the theft of source code.

Adobe is in the process of resetting the passwords of all affected Adobe ID accounts and notifying customers whose credit or debit card information was involved in the security breach. The company is offering U.S.-based customers a one-year complimentary membership in a credit monitoring service.

Adobe has alerted the banks processing customer payments and is working with external partners and law enforcement to address the incident.

According to Arkin, hackers also appear to have accessed the source code of "numerous Adobe products." However, only Adobe Acrobat, ColdFusion and ColdFusion Builder have been named so far.

"Based on our findings to date, we are not aware of any specific increased risk to customers as a result of this incident," Arkin said in a separate blog post, adding that Adobe is not aware of any zero-day exploits -- exploits against previously unknown vulnerabilities -- being used to target Adobe products.

According to Hold Security, more than 40GB of encrypted archives that appear to contain the source code for the Adobe Acrobat and Adobe ColdFusion product lines were found on servers used by cybercriminals who are believed to have also hacked into computer systems of major data brokers Dun and Bradstreet, LexisNexis and Kroll Background America.

The breach appears to have occurred in early August, and it's unclear whether the hackers analyzed the source code or used it for malicious purposes, Hold Security said on its website.

The firm seems to disagree with Adobe on the potential security impact of the source code being stolen.

"Adobe products are installed on most end-user devices and used on many corporate and government servers around the world," Hold Security said in a [blog post]. "While we are not aware of specific use of data from the source code, we fear that disclosure of encryption algorithms, other security schemes, and software vulnerabilities can be used to bypass protections for individual and corporate data. Effectively, this breach may have opened a gateway for [a] new generation of viruses, malware, and exploits."

Adobe could not confirm whether the popular Adobe Reader product was also affected, or if the security breach also resulted in the theft of encryption keys or code-signing certificates.

"Our investigation is still ongoing," the Adobe spokeswoman said.

This is not the first time hackers have compromised Adobe's internal computer systems. Last year, attackers gained access to an Adobe code-signing server and used it to digitally sign malware.

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